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Surveillance and Phytosanitary Measures for Potato Cyst Nematodes
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What are Potato Cyst Nematodes (PCN)?
Potato Cyst Nematodes (PCN) are considered to be quarantine pests because, if not managed, they can reduce yields of potatoes and other host crops such as tomatoes and eggplants by up to 80 per cent. In addition, their presence in a field reduces saleability and export prospects for crops produced in that field. These pests infest soil and are very difficult to eradicate because they can persist, dormant in the soil, for several decades. Two species of PCN include Golden Nematode (Globodera rostochiensis) and Pale Cyst Nematode (Globodera pallida).
Where does PCN exist?
PCN has been previously confirmed in 65 countries worldwide, including parts of Europe, Asia, Africa, North America, Central America, South America and the Middle East. In the United States, Golden Nematode was detected in the State of New York and Pale Cyst Nematode in the State of Idaho. In Canada, Golden Nematode was detected in Newfoundland, British Columbia, Quebec and Alberta while Pale Cyst Nematode has only been detected in a small area in Newfoundland.
How is the presence of PCN determined?
In accordance with relevant international standards, laboratory analysis of soil samples or the roots of symptomatic plants is required to identify PCN. The probability of detection depends on the intensity of the soil sampling scheme adopted and the density of the PCN population in the soil. Confirmation of PCN is based on morphological (shape and size) identification at the microscopic level by highly trained specialists. DNA-based laboratory techniques, such as Polymerase Chain Reaction (PCR), may also be used to further substantiate the results. The revised PCN Guidelines provide some clarity for the uniform interpretation in Canada and the U.S. of suspect and positive PCN samples.
How does the Canadian Food Inspection Agency (CFIA) conduct investigations into PCN detections in Canada?
The process followed by the CFIA following detection of PCN is as follows:
- Historical data from the suspect field on which PCN was detected is immediately investigated.
- As procedures to confirm whether the field is infested with PCN are being conducted, immediate restrictions are placed on the suspect field to prevent potential PCN spread.
- Upon confirmation of a positive detection, where at least two cysts from two different soil samples with one cyst containing viable PCN eggs or juveniles are found, all exposed and adjacent fields are put under various restrictions, along with the infested field, and an intensive soil sampling and testing program is initiated. This intensive soil sampling is often referred to as the delimiting survey and it is conducted to identify the extent of the infestation and the application of appropriate regulatory controls to contain the pest.
- Any additional fields that have been confirmed to be positive through these activities are also investigated.
- All potential pathways of introduction are investigated to determine the source of the infestation, if possible. This includes the movement of all commodities in and out of affected fields, history of field rental, crop rotation and equipment sharing.
Can PCN be eradicated?
Although PCN can be eradicated, it is difficult to achieve this or to confirm its success. Once PCN has infested soil in a particular area, it is possible for the pest to survive for several decades. Eradication of PCN requires a combination of approaches including the prohibition of planting susceptible host plants such as potato, tomato, and eggplant for many years. Strategies such as soil fumigation and the use of resistant potato cultivars may serve to reduce the population of cysts in the soil and do play an important role in a long-term PCN management strategy.
Why were the PCN Guidelines created?
The CFIA and United States Department of Agriculture Animal Plant Health Inspection Service (USDA-APHIS), being the National Plant Protection Organizations (NPPOs) of their respective countries, established these Guidelines to harmonize PCN survey strategies and to implement appropriate phytosanitary measures upon the detection of PCN in either country.
These PCN Guidelines outline the measures and actions that should be taken to contain, control and manage an infestation.
Overall, the PCN Guidelines provide directions to mitigate the risks associated with PCN detections and facilitate continued and predictable movement of material determined not to be infested with PCN.
The vast majority of Canada and the United States are considered not to be infested with PCN and the establishment and maintenance of a consistent and harmonized PCN surveillance approach provides further evidence of this pest-free status.
When were they created?
The PCN Guidelines were first agreed upon and signed by the CFIA and the USDA-APHIS on October 15, 2006. They were subsequently updated in May 2008 and more recently in June 2009.
Why were they amended in 2009?
Both the Canada and the U.S. committed to amending the PCN Guidelines taking into account recommendations from an Independent International Science Panel on PCN.
Amending the PCN Guidelines is necessary to provide specific details on how Canada and the U.S. conduct and implement PCN detection and delimiting surveys as well as implement phytosanitary measures and certification requirements for seed potatoes. In addition, the Guidelines did not include an agreed upon process to release land from regulatory control following a PCN detection. The PCN Guidelines now include direction for the safe removal of restrictions on PCN regulated land after intensive soil sampling and testing is completed. Furthermore, because PCN detections now involve seed production areas (the 2007 detection in Alberta was in a field used for seed potato production), conducting PCN detection surveys on these fields throughout both countries is imperative to provide re-assurance that PCN is not widespread.
According to the PCN Guidelines, what is the difference between an infested field and a suspect field?
An infested field is a field in which Potato Cyst Nematode has been detected and confirmed, meaning at least two cysts from two different soil samples with one cyst containing viable PCN eggs or juveniles are found.
A suspect field is a field in which at least one cyst been detected but where definitive identification and/or confirmation of the cyst as a Potato Cyst Nematode has not yet been made.
How will suspect fields be followed up by the CFIA?
Suspect fields are dealt with in a similar way to infested fields. The CFIA will initiate immediate phytosanitary measures to contain the prospective PCN infestation and to prevent possible spread to non-infested areas. Suspect fields will be sampled and tested on a priority basis in accordance with intensive sampling regimes to confirm if PCN is present.
These measures include restricting the immediate movement of regulated articles from suspect field. If the presence of PCN is confirmed, additional restrictions will be applied to any adjacent and exposed fields unless sufficient survey information is available from those fields as described in the PCN Guidelines.
Again, at least two cysts from two different soil samples with one cyst containing viable PCN eggs or juveniles must be found in order for the field to be considered infested. If results do not show confirmed presence of PCN, then the field must be surveyed a second time. If PCN is not detected in either survey using the intensive soil sampling regime, then the suspect field is no longer suspect and all phytosanitary measures can be lifted.
According to the Guidelines, what is the difference between exposed, adjacent, or non-exposed fields?
An exposed field refers to a field that was associated in one way or another by the movement of soil, equipment, or seed potatoes from an infested field.
An adjacent field is a field or tract of land bordering an infested field and not separated by any major highway, major water course, forested area or non-agricultural area more than 15 yards wide.
If the presence of PCN is confirmed, restrictions are applied to any adjacent and exposed fields in order to contain the PCN infestation and to prevent possible spread to non-infested areas.
Non-exposed fields are fields determined not to be associated with a PCN-infested field. Restrictions are usually not placed on these fields unless it is justified to facilitate the implementation of appropriate phytosanitary measures.
According to the Guidelines, what are trace-back and trace-forward fields?
A trace-back field is a parcel of land that provided propagative material to an infested field. A trace-forward field is a field determined to have been exposed to an infested field by receipt of propagative material from the infested field.
If the presence of PCN is confirmed, restrictions may be applied to any trace-forward fields in order to contain the PCN infestation and to prevent possible spread to non-infested areas. The trace-back fields should be surveyed on a priority basis at the high soil sampling intensity and are not subject to immediate regulatory controls.
According to the Guidelines, what are regulated materials?
Regulated materials include soil, PCN host crops, and any other article that may result in the movement of soil or otherwise of PCN. These materials include, but are not limited to, farm equipment, farm tools, used containers and commodities such as root crops, soybeans, peas, beans, hay, straw, plant litter, nursery stock, bulbs, corms, rhizomes, tubers of ornamental plants, and grass sod (turf).
Regulated materials can only be moved from PCN-regulated areas after they meet the risk mitigation requirements outlined in the PCN Guidelines or through compliance agreements authorized by the respective NPPO.
According to the Guidelines, when are washing and cleaning measures for the movement of equipment from PCN-regulated areas no longer required?
Equipment can only be moved from PCN-regulated areas after it has been cleaned free of soil or disinfected and is accompanied by a movement certificate, unless justification for reduced sanitation requirements are met.
In the case of an infested field, one negative viability assay and one negative bioassay at the minimum of 45 lbs per acre each is required before reducing equipment cleaning requirements.
In the case of an adjacent or exposed field, one negative survey using Method A or two negative surveys using Method B is the minimum required before the reduction of equipment cleaning requirements can be considered.
According to the Guidelines, what is a viability assay survey and what is a bioassay?
A viability assay survey is undertaken using soil samples from fields where PCN is apparently no longer alive and is an indication that the content of the cysts is dead. The viability status of the eggs within the cysts is determined either through a visual assessment of viability by trained nematologists or through the use of viability staining. The PCN Guidelines permit the use of Medola's Blue Stain or Iodine for differentiation between viable and non-viable PCN eggs.
Determining the viability of the eggs is important as cysts with viable eggs may persist in the soil for approximately 30 years.
A bioassay is another method to assess and provide confidence that the content of any remaining cysts is dead, no longer able to cause an infestation. It is usually conducted under a controlled environment to maximize any possible multiplication of PCN and to contain any infestation.
According to the PCN Guidelines, what is the difference between Method A and Method B soil sampling?
The key difference between the two methods of soil sampling is the rate of soils collected and sampled. Method A requires a minimum of 15 lbs of soil per acre to be tested while Method B requires a minimum of 5 lbs of soil per acre to be tested. The only other difference is that the sampling grid cell can be larger when using Method B; it can be up to 36 yd2 while Method A requires the grid cell be a maximum size of approximately 21.5 yd2.
Both methods of soil sampling for PCN include sampling the entire field in a fixed grid pattern. Both methods also require that for hand sampling, the length of the grid cell should not be greater that 2.5 times the width and for rectangular shaped grid cells the longest dimension should be parallel to the direction of cultivation.
According to the PCN Guidelines, how is a PCN-regulated field released from regulatory control?
The PCN Guidelines describe in detail the phased reduction of phytosanitary measures that are required to deregulate infested, adjacent and exposed fields.
In summary, infested fields are eligible for the lifting of some restrictions when intensive surveys, viability assays and bioassays are completed with no live PCN detections. Seed potato production in a field which was determined to be infested with PCN is not allowed if they are going to be planted outside of the PCN regulated area. If results are negative, an additional four full field surveys must be conducted using a minimum of Method A before most restrictions can be lifted.
Adjacent and exposed fields are eligible for consideration to remove the soil cleaning requirements when at least one full field survey is conducted using Method A or two surveys are conducted using Method B with negative results for PCN. All regulatory controls on exposed fields can be removed after an additional full field survey is conducted using Method A or two additional surveys are conducted using Method B with negative results. However, regulatory controls placed on adjacent fields may not be removed until the bioassay associated to the corresponding infested field is negative.
According to the Guidelines, what happens if there is another PCN detection confirmed in Canada or the U.S.?
The NPPO of the country with a new PCN detection will immediately conduct investigations to identify exposed fields to be included in the delimiting survey and the interim regulated area.
In cases where the PCN-infested field was used for seed potato production, information should be collected from the seed lots produced on the infested farm units.
Based on information gathered from investigation activities, the NPPO of the country with a new or suspect PCN detection will initiate immediate phytosanitary measures to contain the PCN infestation and to prevent spread to non-infested areas. Although the NPPO of the other country will be informed without delay, these measures will not involve nation or state or province-wide restrictions on the movement of potatoes between the two countries.
When will these PCN Guidelines expire?
These PCN Guidelines will remain in force unless terminated by either NPPO after giving 60 days written notice to the other NPPO. The PCN Guidelines may also be terminated by mutual consent as of a date approved in writing by both NPPOs.
How will the revised PCN Guidelines be communicated to growers?
The PCN Guidelines document will be communicated to growers through national industry associations and their regional counterparts. The CFIA will also continue to keep industry informed through Web updates to the CFIA Web site and through information bulletins.
This document contains imperial measurements. Corresponding metric measurements can be found in the 2009 Guidelines on Surveillance and Phytosanitary Actions for the Potato Cyst Nematode (PCN Guidelines).
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